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A function that utilizes a dictionary returns the KeyFile error "\n" when I use DNA strings from a text file, but not when I manually type a DNA string:


DNA = open(r"C:\Users\CP\Desktop\Python\rosalind_revc.txt","r")
DNA = DNA.read()
DNA.replace(' ','')
print(DNA)
# Output works when I manually type a DNA string, such as the one below in the comment
# DNA = "TCAGCAT"

def complement(s): 
    
    # Create a dictionary with all the complementary base pairings
    basecomplement = {'A':'T','C':'G','G':'C','T':'A'}
    
    # Turn the input DNA into a list
    letters = list(s)
    
    # Use the dictionary to replace each list element
    n = [basecomplement[b] for b in letters]
    
    # Make the function return the list as a string
    # We want no spaces in the new DNA string, so there are no spaces inside
    # the quotation marks--that's where the "separator" is.
    return ''.join(n)

def revcom(s):
    return(complement(s[::-1]))

DNA_revcom = revcom(DNA)

print(DNA_revcom)

I am new to Python programming, so I appreciate any feedback!

Childs_Palace
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  • Does this answer your question? [How can I remove a trailing newline?](https://stackoverflow.com/questions/275018/how-can-i-remove-a-trailing-newline) – Nick Jan 27 '21 at 02:13

1 Answers1

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The line in the file has a newline character, unlike the string you manually typed in. So you need to remove the newline character, which you can do with rstrip, like so:

DNA = DNA.read().rstrip()
mdml
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